Doing web dev in .NET nowadays for me is mostly creating HTTP/JSON/REST APIs and using whatever FE framework you like to interface it (for me that is React or NextJS). The keyword you want to search for is "ASP.NET WebApi" or - more modern - "ASP.NET minimal API".
You could still do .NET MVC server-side rendering using "Razor" (the markup language in ASP.NET MVC - search for "ASP.NET MVC Razor".
(Hybrid Blazor where you use both server and client possibly in the exact same assembly/project is where most of the worst Blazor mistakes lie, but those aren't the mistakes of Silverlight, those are the mistakes of ASP Classic before .NET where you can be easily confused by new versions of the which bit of this is `runat="server"` and which bit is `runat="client"` and easily and accidentally create wild RPC ravioli/spaghetti code.)
(I don't mind outdated for .NET stuff, nearly everything from enterprise vendors looks like it just jumped out of WinXP anyway.)
There were definitely some quirks and issues early on but they've done a pretty good job at smoothing that stuff out since it's gone through two LTS version of .NET.
The pipeline for something like that is click->js/wasm websocket->server code->websocket->ui updates. If you're doing something absurd on the back end when a checkbox is clicked, sure 1-2 seconds but that's a developer problem, not a Blazor problem. If you put me in front of a React app, I'd probably do something stupid like that too because I don't have much experience with it.
I suspect your complaint is more related to .NET/Blazor making it easier for less experienced developers to develop a working site/page with a lot of spaghetti where that same developer would struggle to create the same page in another ecosystem. If you compare to equally senior/experienced developers in different frameworks, I suspect you'd see the same basic performance from the two platforms up until a scale that very few of us are actually working in. Blazor can be quite fast if you don't write bad code.
I find a lot of the complaints about .NET to be that it enables developers who write bad code to get things done inefficiently instead of not being productive at all. IMO, having senior developers doing code reviews is pretty essential if you have junior developers on a team but the ability to build something, even if poor, can really accelerate the learning process when a senior person can look at a complete project, point out the issues and show the difference that the corrections make.
Sorry for the rant and sorry if this doesn't really apply to you specifically.
I'm looking for something that will make me "wow, Blazor can be used to build great apps!" or "ok has advantages over the React/Vue etc. equivalent".
Because if there aren't any, in similar thinking with parent, I'm afraid that it won't catch up and it'll go the way of silverlight, so I refuse to invest any time.